#23 - A scientific study provides evidence that crows are

[KelseyWoods]

Hi cjv!

As you determined, the literal negation of answer choice (A) would be: "none of the crows that shrieked at and dive-bombed people wearing the masks were not among the crows that had been trapped." But careful with how you interpret the meaning of that statement because it contains a confusing double negative!

Your interpretation was that this said that none of the dive-bombing crows were trapped. But the negation actually says that none of the dive-bombing crows were NOT trapped. That means that all of the dive-bombing crows were trapped. If all of the dive-bombing crows were the ones that had previously been trapped, that would attack the argument that crows pass on information to other crows.

When a negation creates a double negative like we have here, you have to be really careful with how you interpret it because those double negatives are definitely tricky!

Hope this helps!

Best,
Kelsey

[cjv]

Thank you Kelsey!

However, I am still having a problem with the negation interpretation. Your explanation makes sense, but help me a little more.

Negating answer choice A "NONE of the crows that dive-bombed were NOT among those the crows that were trapped. Why do I still interpret this as if the crows that dive-bombed were not apart of those that were trapped.

If I really simplify the answer choice to "NONE were NOT trapped" it makes complete sense because then they are apart of the group that was trapped.

[Rachael Wilkenfeld]

Hi cjv,

Let's break things down a bit. We have two logical opposites for quantity here. We have some crows, or the opposite none of the crows/no crows. We also have the logical opposites of trapped/not trapped crows.

When we take the logical negation of answer choice (A), we only negate the quantity term. If we negate multiple terms, we'll end up negating a different statement.

Let's look at how this works with a more direct example:

Statement: Some Cleveland Browns players were not in the Pro Bowl. This means that there is at least one player on the Cleveland Browns that did not make the Pro Bowl. So anywhere from 1-100% of the Cleveland Browns were out of the Pro Bowl.

Correct negation: No Cleveland Browns players were not in the Pro Bowl. This means that there are no Cleveland Browns players that did not make the Pro Bowl. This is the logical opposite of some being left out---here none are left out. They are all in. 0% of Cleveland Browns did not make the Pro Bowl.

Overnegation (INCORRECT): No Cleveland Browns players were in the Pro Bowl. This example negates both "Some" at the beginning and the "were not in the Pro Bowl." This one means that 100% of the Cleveland Browns players were not in the Pro Bowl. That's not the logical opposite of our original statement---it's included in the original statement.

Let's turn back to our friendly crows.

Statement: Some of the dive-bombing crows were not among those trapped. This means 1-100% of the crows were not trapped. Our negation should say that 0% were not trapped.

Negation: None of the dive-bombing crows were not among those trapped. This means that none (0%) of the crows were not-trapped, so all the dive-bombing crows were trapped. This negation weakens the conclusion that the crows could communicate to others because they could have just been reacting to their own experiences.

Hope that all helped.

[lavalsat]

I can see how answer A is the correct choice- but I am having trouble with the fact that LSCA expects test takers to assume that crows shrieking and dive bombing equals crows perceiving something as threatening. I feel like that assumption would require at least a basic knowledge of zoology. I'm not sure why it is expected for the average test taker to make that leap. Animals could be shrieking and dive bombing for countless other reasons.

My main question is: If we decided that we cannot make that assumption, isn't answer B also something this argument depends on? Am I missing another reason answer B is wrong?

[Adam Tyson]

As I see it, lavalsat, the problem with answer B is the use of "always," which is a very strong word that would require some very strong evidence to make it necessary. Doesn't the author only have to assume that sometimes crows behave that way when they feel threatened? You're right that the author is making that assumption, too, but we don't have to know anything about zoology to see that. If answer B had said that crows who behave that way at least sometimes do so because they perceive a threat, then it would be a great answer. That's why B is such an attractive trap answer!

Here, the author argued that crows not only recognize a threat, but they can pass on that info to other crows. How did they get that idea? Only if they assumed that at least some of the crows who behaved that way were not the same crows who had originally been trapped by people in those masks. Otherwise, there would be no reason to believe the info ever got passed on.

There can be many assumptions in an argument. You identified one, and answer A identified another. Another would be that crows do not always consider people to be a threat, and another would be that they do not see something threatening in the masks themselves. If either of those last two were false, then there would be no evidence that any crows recognized anything!

[andrewb22]

How would you negate answer (E)?

[Poonam Agrawal]

Hi Andrew,

You can negate answer choice (E) in two parts:

1.) Crows cannot distinguish between people wearing the masks and people who are not
2.) Crows can recognize individual human faces

The first part of this answer choice makes it sound like a tempting pick, but the second part is completely irrelevant to the argument. It doesn't really matter whether or not crows can recognize individual faces, all we care about is if crows recognize cavemen as a threat and can communicate this to other crows. Because we're looking for an assumption that the argument depends on (i.e. a necessary assumption), answer choice (E) doesn't do the job because it is not necessary for crows to not be able to recognize individual faces for the conclusion to follow.

James sums this up nicely above:

However, (E) is actually not necessary to the argument, because the premises given in the stimulus tell us about people wearing the same cavemen masks when they trap the crows as when they approach the crows again years later. Whether crows can tell the difference between people wearing masks or not, or whether they can recognize individual faces, is irrelevant: all we know is that they recognized the cavemen masks and reacted to them as a threat, and that we have to fill the gap of "communicating" that threat. This is what (A) accomplishes, while (E) serves only as a red herring.

[smtq123]

I have two doubts:
1) The argument mentions that crow "CAN" pass on the information. It is not a mandatory requirement because of the use of the word "CAN"; so if negating A implies that crow didn't pass the information, then the argument didn't fall apart!
2) WHAT IF the trapped crow's behavior of shrieked and dive-bombed is NOT a threatening response as we don't know it from the argument!
Appreciate your reply!

[evelineliu]

Hi there,

• For (A), if the attacking birds were all trapped before, then there is no evidence that the crows pass the information about threatening people along. The author must be assuming that the attacking birds were not originally trapped. That is what makes (A) correct.

• Although the argument didn't tell us, we can use our common sense that crows would shriek and dive-bomb as a threat response. At the very least, it shows us that the crows can recognize threatening people.

Best,
Eveline

[Henry Z]

I have some thoughts on (B). I think it’s wrong not because of “always”, but because of reversal.

The assumption is that if crows shriek and dive-bomb, it’s always when they perceive threat. It’s a concept shift, but with a direction: shriek and dive-bomb —> perceive threat.

It doesn’t have to assume that when perceive threat, crows always shriek and dive-bomb, which is what (B) says.

Can someone confirm my thoughts?